WASHINGTON — Large new cuts in defense spending would “terribly weaken” U.S. national security, Defense Secretary Leon Panetta said Tuesday as he and Secretary of State Hillary Rodham Clinton used a rare joint interview to argue that the nation cannot afford to keep playing partisan chicken with its finances.

Panetta expressed optimism about progress by American-led forces against the Taliban in Afghanistan and by NATO forces in support of anti-government rebels in Libya. He cited those conflicts as examples of why severe cuts to spending on defense and diplomacy would be dangerous.

Panetta said the Pentagon is prepared to make $350 billion in cuts during the next 10 years, as agreed by Congress. But he warned of dangers to the national defense if bigger reductions are required.

The recent deficit compromise reached between the White House and Congress set up a special bipartisan committee to draft legislation to find more government cuts. If the committee cannot agree on a deficit reduction plan by year’s end, or if Congress rejects its proposal, it would trigger $500 billion in additional reductions in projected national security spending.

“This kind of massive cut across the board, which would literally double the number of cuts that we’re confronting, that would have devastating effects on our national defense; it would have devastating effects on certainly the State Department,” Panetta said.

Clinton said Americans should understand that in addition to preserving military strength, it is in the nation’s security interests to maintain the State Department’s role in diplomacy and development. She suggested that the political stalemate over spending cuts has put that in jeopardy.

“It does cast a pall over our ability to project the kind of security interests that are in America’s interests,” she said.

Clinton and Panetta appeared together at National Defense University in an interview conducted by Frank Sesno, director of the School of Media and Public Affairs at George Washington University. Several members of the audience, which included military and civilian officials, also asked questions.

In deploring a fresh wave of violence in Iraq that killed at least 70 people Monday, Clinton also suggested that the Iraqi government is not doing all it can to prevent terrorist acts.

“The Iraqis themselves have more capacity than they did have, but they’ve got to exercise it,” she said. “And we spend a lot of time pushing our friends in the Iraqi government to make decisions, like naming a defense minister and an interior minister, so that they can be better organized to deal with what are the ongoing threats.”

Panetta was adamant that severe new budget cuts would undercut the nation’s role in the world.

“Very simply, it would result in hollowing out the force,” he said, alluding to reductions made in the aftermath of the Vietnam War that left Army units undermanned and ill-equipped.